ABSTRACT ? Project 1: Impact of co-occurring ADHD symptoms on early risk factors and routine screening for ASD in primary care Approximately 40-60% of children with autism spectrum disorder (ASD) also have co-occurring attention deficit hyperactivity disorder (ADHD) or elevated symptoms of ADHD, which are associated with a range of adverse clinical outcomes compared to those of children with ASD alone. These impairments include greater emotional difficulties, tantrums, conduct problems, more severe ASD symptoms, greater difficulty interacting with peers, and poorer adaptive behavior. Critically, the presence of co-occurring ADHD symptoms is also associated with later diagnosis of ASD, thus limiting access to crucial early intervention. Despite these adverse trajectories of children with ASD+ADHD, very little is known about how the co-occurrence of these clinical conditions develops in early childhood. The overall goal of Project 1 is to characterize both the risk factors for and the early emergence of co-occurring ADHD symptoms in young children at risk for ASD and to understand how these symptoms impact early detection and progression of ASD. This is significant from a public health perspective since this knowledge could help reduce existing disparities in access to early diagnosis and treatment. This project will take advantage of existing infrastructure and expertise to screen and monitor the population of young children seen in pediatric primary care clinics within the Duke University Health System (N ~ 2800 patients annually). In doing so, we will be able to prospectively identify children at risk for ASD and simultaneously collect data on ADHD and related behaviors starting as young as 18 months. Information related to pre- and post-natal risk factors will be obtained from children's electronic health records. We will then monitor and characterize the progression of both ASD and ADHD symptoms across development, identifying how ADHD symptoms impact ASD screening and diagnosis and later developmental outcomes. Data from Project 1 will enable the development of more effective strategies for early detection of children with ASD and co-occurring ADHD symptoms, which could reduce the delay in early detection and increase access to early treatment.